higher standby voltage on a phillips tv power supply

[DjKrish]

Hi, i have a phillips 46pfl6606h tv here with no power. fuse blown, power ic blown, diodes blown due to excessive voltage. Ok now i have fully repaired the high side of the psu. As for the low side, on the standby voltage there suppose to be 3.3v but its showing 6v. Is that something i need to be worried about? According to the picture i attached, the marked diode was blown, and it says 7.5v zener diode, so i replaced with 7.5v zener diode. Unless its a 3.3v zener diode? Even i measured at the photo coupler leg it measured 6v.

[budm]

Re: higher standby voltage on a phillips tv power supply

If that Zener d103 is blown it means the 300V is dump into the IC when it shorted out,
Did you verify that the opto PC101 and D104 are still OK?
Also, the meter and the battery of the meter iare OK?
If it is truly 6V output, do not leave it connected to the main board for now until it is verified.
LNK362 SMPS IC.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

If that Zener d103 is blown it means the 300V is dump into the IC when it shorted out,
Did you verify that the opto PC101 and D104 are still OK?
Also, the meter and the battery of the meter iare OK?
If it is truly 6V output, do not leave it connected to the main board for now until it is verified.
LNK362 SMPS IC.

LNK362 replaced. zener replaced. opto replaced. d104 replaced as well. Meter is using brand new battery, its a fluke.

These are the components that was shot. Now high side seems to be ok though. Butttttttt, 3.3 is turning on the high side.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

Or maybe the zener diodes description is incorrect on the circuit diagram. I dont know. I may be wrong. Ive seen circuit diagrams even though correct model but incorrect part numbers.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

Anyone?

[budm]

Re: higher standby voltage on a phillips tv power supply

That 7.5V Zener is the correct value, if you look at the internal circuit of the SMPS IC pin 3 (BP), the IC already has the internal 6.3V Zener to clamp down the output of the internal 5.8V regulator output, basically that external 7.5V is connected in parallel with internal 6.3V Zener so that external 7.5V is not really needed for the circuit to function, it is just and added protection.
At this point it looks like the power supply is not regulating.
What did you replace the OPTO PC101 with?
What Voltage do you get when measure between the two leg of the OPTO on the LED side?
What Voltage do you get when measure between the two leg of the OPTO on the Photo-Transistor side?
Is C107 tested good?
Please attach good clear hi-res of the whole top and bottom side of the power supply board for us to look at.
Did anyone else work on this board before you?

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

That 7.5V Zener is the correct value, if you look at the internal circuit of the SMPS IC pin 3 (BP), the IC already has the internal 6.3V Zener to clamp down the output of the internal 5.8V regulator output, basically that external 7.5V is connected in parallel with internal 6.3V Zener so that external 7.5V is not really needed for the circuit to function, it is just and added protection.
At this point it looks like the power supply is not regulating.

What did you replace the OPTO PC101 with?
What Voltage do you get when measure between the two leg of the OPTO on the LED side?
What Voltage do you get when measure between the two leg of the OPTO on the Photo-Transistor side?
Is C107 tested good?
Please attach good clear hi-res of the whole top and bottom side of the power supply board for us to look at.
Did anyone else work on this board before you?

What did you replace the OPTO PC101 with? I replaced with PC817

What Voltage do you get when measure between the two leg of the OPTO on the LED side? 0.098V

What Voltage do you get when measure between the two leg of the OPTO on the Photo-Transistor side? 4.58V

Is C107 tested good? yes its good

Please attach good clear hi-res of the whole top and bottom side of the power supply board for us to look at. Uploaded
Did anyone else work on this board before you? Definitely not.

[budm]

Re: higher standby voltage on a phillips tv power supply

What did you replace the OPTO PC101 with? I replaced with PC817

What Voltage do you get when measure between the two leg of the OPTO on the LED side? 0.098V

What Voltage do you get when measure between the two leg of the OPTO on the Photo-Transistor side? 4.58V

Is C107 tested good? yes its good

Please attach good clear hi-res of the whole top and bottom side of the power supply board for us to look at. Uploaded
Did anyone else work on this board before you? Definitely not.

"What Voltage do you get when measure between the two leg of the OPTO on the LED side? 0.098V" This LED is not on at all, at 6V output this LED in the OPTO should be on, it should be about 1.5 ~ 1.8V) to turn on the Photo Transistor to regulate the output, if U301 is not on then LED will not be on so you need to check surrounding circuit,
Check the LED of this OPTO in diode mode and in Ohm mode to see what it shows.

BTW, my request: "Please attach good clear hi-res of the whole top and bottom side of the power supply board for us to look at." I still need those full straight shots pictures of the whole board, your pictures only show partial pictures of the board.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

Hi heres the photos. I tested the OP with analogue muiltimeter the traditional way, the led only has reading one side as usual whereby the transistor side no reading both way.

[budm]

Re: higher standby voltage on a phillips tv power supply

Hi heres the photos. I tested the OP with analogue muiltimeter the traditional way, the led only has reading one side as usual whereby the transistor side no reading both way.

So you do not have Digital meter? You should get one. Analog meter has low input resistance so it will affect the Voltage readings when trying to read Voltage in high resistance circuit. https://www.quora.com/What-is-the-vo...loading-effect, https://www.allaboutcircuits.com/tex...sured-circuit/
if you look at the schematic, it has resistors connected in parallel withe the LED of the OPTO so the meter should show resistance in both direction, look at the schematic.
You also need to test Voltages around U301, U301 may be bad and not turning on.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

So you do not have Digital meter? You should get one. Analog meter has low input resistance so it will affect the Voltage readings when trying to read Voltage in high resistance circuit.
if you look at the schematic, it has resistors connected in parallel withe the LED of the OPTO so the meter should show resistance in both direction, look at the schematic.
You also need to test Voltages around U301, U301 may be bad and not turning on.

I have 5.6V and 2.5V reading on Cathode and Reference on the U301 using a digital meter. Tested the resistors, they are accurate reading. Just curious, can AZ431 be substituted with TL431 if its faulty?

[budm]

Re: higher standby voltage on a phillips tv power supply

Can you look at your board and see if U301 is actually AZ431L (1.24V Adj shunt regulator) or it is TL431 (2.5V)?

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

Can you look at your board and see if U301 is actually AZ431L (1.24V Adj shunt regulator) or it is TL431 (2.5V)?

At the board its AZ431L. So based on the voltage, do u think the regulator is shot?

[budm]

Re: higher standby voltage on a phillips tv power supply

At the board its AZ431L. So based on the voltage, do u think the regulator is shot?

Yes.
Since we know that U301 is rated at 1.24V, that means the output of the power supply is designed to be at 3.3V.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

Yes.
Since we know that U301 is rated at 1.24V, that means the output of the power supply is designed to be at 3.3V.

Okay noted, thank you. will get it replaced and update he how it went. The part is not available anywhere in my country for now, need to order. While in the meantime, i read somewhere we can put a couple of zener diodes to perform a temp test to see if the circuit works as it should? Using zener diodes as a substitute to shunt regulator. Is that possible?

[budm]

Re: higher standby voltage on a phillips tv power supply

Okay noted, thank you. will get it replaced and update he how it went. The part is not available anywhere in my country for now, need to order. While in the meantime, i read somewhere we can put a couple of zener diodes to perform a temp test to see if the circuit works as it should? Using zener diodes as a substitute to shunt regulator. Is that possible?

You can try 1K in parallel with the U301 to simulate current flow through the OPTO LED, you should see Voltage drop down from 6V, or you can use 1K pot.

[momaka]

Re: higher standby voltage on a phillips tv power supply

Another suggestion, though I'm not sure how well it would work (or if at all):
Replace the AZ431L with a regular 431 (i.e. TL431) if that's all you have in stock. Then increase the value of the "lower" resistor in the resistive divider connected to the TL431 control/reference pin accordingly for 3.3V output. Looks like the lower resistor for that divider is R307.

The idea is that when you have 3.3V on the output of the PSU, the reference pin should now be at ~2.5V for the regular TL431.

I can't quite read the values on those SMD resistors completely, but looks like the lower resistor has "1201" printed on it - i.e. 1.20 KOhms? If that's the case, try a resistance of around 6.012 KOhms (or thereabouts) with a regular TL431. That should regulate to 3.3V output, more or less (may need to increase or slightly decrease the value of the "6.012"-KOhm resistor, to get desired output.) Putting together 10K, 22K, and 51K resistors in parallel should give about 6.058 KOhms, which might be just close enough... that is, provided R307 is indeed 1.20 KOhms. Please check before trying anything.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

Another suggestion, though I'm not sure how well it would work (or if at all):
Replace the AZ431L with a regular 431 (i.e. TL431) if that's all you have in stock. Then increase the value of the "lower" resistor in the resistive divider connected to the TL431 control/reference pin accordingly for 3.3V output. Looks like the lower resistor for that divider is R307.

The idea is that when you have 3.3V on the output of the PSU, the reference pin should now be at ~2.5V for the regular TL431.

I can't quite read the values on those SMD resistors completely, but looks like the lower resistor has "1201" printed on it - i.e. 1.20 KOhms? If that's the case, try a resistance of around 6.012 KOhms (or thereabouts) with a regular TL431. That should regulate to 3.3V output, more or less (may need to increase or slightly decrease the value of the "6.012"-KOhm resistor, to get desired output.) Putting together 10K, 22K, and 51K resistors in parallel should give about 6.058 KOhms, which might be just close enough... that is, provided R307 is indeed 1.20 KOhms. Please check before trying anything.

Ive already ordered the part So waiting for it and see how it goes. As for now i dont have the TL431 either. So i better use the original part since its on the way.

[DjKrish]

Re: higher standby voltage on a phillips tv power supply

Ok update time. Parts arrived. Fitted, checked for voltage, 3.3v was there perfectly. Hooked up to main board, standby light was there. Turned on tv, light was there, screen was there, then came a high pitch sound from power supply. I turned off the power, and then theres no standby light anymore. Unhooked the smps, tested for voltage again, its there 3.3v and nothing changed. What else could be wrong? How do i short the power supply on its own to turn it on, so that i can check all the output voltages? Suspect the high pitch sound came form the transformer thats connecting to the backlight.

[budm]

Re: higher standby voltage on a phillips tv power supply

Ok update time. Parts arrived. Fitted, checked for voltage, 3.3v was there perfectly. Hooked up to main board, standby light was there. Turned on tv, light was there, screen was there, then came a high pitch sound from power supply. I turned off the power, and then theres no standby light anymore. Unhooked the smps, tested for voltage again, its there 3.3v and nothing changed. What else could be wrong? How do i short the power supply on its own to turn it on, so that i can check all the output voltages? Suspect the high pitch sound came form the transformer thats connecting to the backlight.

Well, you have more than one problem, the 3.3V is fixed but now you have another problem so just have to do more troubleshooting.
Try disconnecting the backlights LED connector and see what happen.